The invention relates to an electromotive adjustment device with a rotor comprising a magnetized rotary body and with a U-shaped stator whose legs form the pole shoes and whose yoke interconnects the two legs, the angular position of the rotor being adjustable by means of the stator current.
Such a device is known from U.S. Pat. No. 5,624,100, issued Apr. 29, 1997. In this known adjustment device, the U-shaped stator is integrally formed from a highly permeable material such as iron, steel, sintered iron, or isotropic magnetic steel. The stator is electrically excitable by means of a single-strand exciter coil. The exciter coil is arranged on the yoke of the stator. This known device is designed in particular for adjusting a throttle plate in the suction line of an internal combustion engine. In this application, a strongly varying torque with high overload torques is to be provided by the electromotive adjustment device over the range of angles of rotation of the rotor because of the air flow in the suction line. A high overload torque is also to be applied partly on account of ice deposits or pollution. The known device must be designed to deal with the operational condition which requires the highest magnetic flux. This leads to a large diameter of the stator, and thus to a high weight. The required magnetic flux is particularly great when a widely opened throttle plate is to be opened yet further at a high stator current, or when an almost closed throttle plate is to be closed yet further at a high stator current. The maximum range of the angle of rotation of the rotor is smaller than 180.degree..